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Effect of processing conditions on the development of morphological features of banded or nonbanded spherulites of poly(3-hydroxybutyrate) (PHB) and polylactic acid (PLLA) blends.


The quantities of plastic waste are increasing in all places of the world as the production and consumption of plastic materials. Most of these plastic materials are produced from raw oil (petrols). However, the excess fabrication of plastic materials (polymers) resulted in increasing the price of oil since the oil resources are limited. Alternatively, most of plastic materials are formed from petrochemicals such as; polyethylene (PE), polypropylene (PP), polyvinyl chloride, and polystyrene (PS). Plastic materials are widely used for different practical applications such as; household, auto parts, building materials, and packaging of food, seeing that their processing, physical properlies and durability are excellent. However, the main disadvantage of these materials is its inherent toxicity and pollution of air and groundwater caused by the retention of nonbiodegradable waste plastic, which prevents its wide practical applications. Hence, the issue of eliminating plastic waste is imperative because of the increasing environmental concerns, which has invoked extensive studies on development of recycling of plastics in recent years.

Nowadays, there are several ways to be settled for disposal of waste plastic.

Recycling of plastics again by rearranged according to their types and colors which are expensive. This requires cleaning after handling and arrangement according to their types and colors. Moreover, the physical properties of recycled plastics are not good as the first use.

Recycling of plastics by chemical decomposition. This method requires a large amount of thermal and electrical energy, which leading to remarkable high cost.

Recycling of plastics by burning. This method leads to raising some toxic gases associated with increasing temperature, such as carbon dioxide. Applying of such methods brings about big problems, like rising the earth temperature which is known as a global warming.

Recycling of plastics by buried in landfills without biodegradation. This waste buried in the earth without any exploitation leading to pollution of groundwater.

In the recent years, attracted attention has been made by many scientists to solve this problem and to produce new biodegradable polymer materials like; PHB, polylactic acid (PLLA), starch and cellulose. PHB or PLLA are two of the attractive polymers that can be used to overcome these problems due to their natural biodegradability. These polymers are produced from renewable natural sources such as; date syrup, sugar cane, and sugar beet, i.e., fermentation of micro-organisms with natural fats, oils, molasses, date syrup and some minerals (1-5). PLLA and PHB could be totally degraded in aerobic or anaerobic environment throw 2 months up to 3 years (1-3). After purification, the lactic acids are polymerized by using extruder and catalysts to form a high molecular mass of PLLA. PLLA has both a hydroxyl group and a carboxylic acid group similar to PHB. Furthermore, both, PLLA and PHB is optically active (6-8), water and oil resistant and linear aliphatic polyester. PHB is a partially crystalline material with high melting temperature and high degree of crystallinity (1-3). On the other hand, PHB belongs to the family of Polyhy-droxyalkanoates (PHAs) and has physical and mechanical properties comparable to those of isotactic polypropylene (iPP). Moreover, PHB and PLLA blends could be used for short term packaging in the food industry, in particular for deep drawing articles and thennoformtd products such as; drink cups, take-away food trays, containers and planter boxes for surgical materials like; sutures and bone implants (screws, pins, plates and fixation rods, etc) pharmaceutical, cosmetic, textiles industries and agricultural films (1-6). However, there are several problems to be settled for practical applications in both materials. For instance; brittleness, higher glass transitions, poor mechanical properties and slower crystallization rate, compared to synthetic polymers such as; polystyrene (PS), polypropylene (PP) and polyethylene terephthalate (PET). Due to these reasons, PHB and PLLA blends cannot be used for many practical applications, especially for food sector as packaging like depth drawing article. We mixed PHB with highest crystallization kinetics and PLLA with lowest crystallization kinetics, since the chemical composition of both is similar. The chemical structure of PHB is:

[[-- O--CH(CH3) --CH2--(C = O) --].sub.n] (1)

and chemical structure of PLLA is:

[[--O--CH(CH3)--(C = O)--].sub.n] (2)

Polymer blends have more attractive attention in the last decades. The polymer blending is a good economic method, which can develop new materials with special properties such as; greater ductility, stronger moduli and higher mechanical strength. If two polymers are immiscible with each other, i.e., two glass transition temperatures or two crystallization temperatures appears in the blends and the mechanical properties of the materials are weakened. However, (PLLA/PHB) blends are crystalline/crystalline polymer. Their properties and miscibility depend on the polymer molecular weight, blend composition, chemical or physical cross linked interactions with each other, morphology and processing conditions. The crystalline morphology depends on the crystallization conditions since their components could be crystalline at a wide crystallization temperature range. It has been found that PLLA is immiscible with PHB (higher molecular weight) (7-11), poly(butadiene-co-acrylonitrile) (NBR) (12), poly(p-dioxanone) (13), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-co-PHV) (14), poly (vinyl alcohol) (PVA) (15), poly(butylene succinate) (PBS) (16), poly (caprolactone) (17), poly(ethylene succinate) (18, 19) and thermoplastic starch (20). Conversely, PLLA is miscible with poly(vinyl acetate) (PVAc) (21) and polyethylene oxide) (21). On the other hand, PHB is immiscible with ethylene-propylene rubber (EPR) blend (22) and synthetic atactic polyhydroxybutyrate (a-PHB) (8). Now, PHB is miscible with PVAc (22) and poly(ethylene oxide) (PEO) (23). Both PHB and PLLA are semicrystalline polymers and consist of two different phases (amorphous and crystalline). By addition of some polymers to an immiscible binary polymer blend, these polymers make as a simple compatibilizer. Both poIy(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA) are immiscible, but with the addition of a suitable amount of polyvinylidene fluoride (PVDF), the miscibility with both PMMA and PEMA could be improved (24). PHB is immiscible with polyepichlorohydrin (PECH), but polyethylene oxide (PEO) is miscible with PHB and PECH (25). Another example, PHB is immiscible with PMMA, but PEO is miscible with PHB and PMMA. Therefore, the completely miscible blend is formed by adding PEO to PHB and PMMA (26). Since the blend of PHB and PLLA is immiscible (7-9), the addition of PVAc to (PLLA and PHB) blends makes it miscible. Therefore, the purpose of this study is to prepare different types of blends from two semi crystalline polymers; PLLA and PHB with and without PVAc to develop of new biodegradable polymer blends, used for different short term packaging in the food and surgical industry, as a replacement of the nonbiodegradable petrochemicals. The structure, morphology, crystallization, melting behavior and miscibility of blends have been investigated by polarized optical microscopy (POM), differential scanning calorimeter (DSC), wide angle X-ray diffraction (WAXD) and FTIR spectroscopy. Furthermore, correlations between the evolution of the microstructure (morphology) and miscibility of blends are studied.



PHB crystallinity 60% ([M.sub.w] = 2.3 x [10.sup.5] g/mol) and PLLA crystallinity 40% ([M.sub.w] = 2.2 x[10.sup.5] g/mol) were supplied from Biomer [R], Germany. PVAc ([M.sub.w] = 0.51 x [10.sup.5] g/mol) was purchased from Sigma-Aldrich Chemicals.

Preparation of Blends

The compositions of PHB/ PLLA/ PVAc blends were prepared with different weight ratios as follows: (25/75/0), (50/50/0), (75/25/0), (22.7/68.1/9.1), (45.4/45.4/9.1), (68.1/22.7/9.1). The sample codes and compositions of these composites was given in Table 1. All blends were prepared by dissolving components together in hot chloro form at 50 [degrees] C, and then the solution was cast in a Petri dish to prepare the casting films. The samples were dried at 60[degrees]C for 24 h to remove any residual solvent completely. The chemicals structures of PHB and PLLA were shown at Scheme 1.


Differential Scanning Calorimetry. DSC is an important technique to study melting and crystallization behavior of polymers. A thermal analysis was carried out with a differential scanning calorimeter (Schimadzu-DSC 50, Japan). All samples of 5 [+ or -]0.1 mg were sealed in an aluminum sample pan for DSC. Samples were kept under a dry nitrogen atmosphere. DSC analysis was carried out from room temperature to 200 [degree] C at heating and cooling rates of 10 [degree] C [min.sup.-1]. Besides, the analysis of DSC curves was carried out for the second heating run data to examine the melting temperature (Tm) and the cold crystalliza tion temperature (Tcc).

Polarized Optical Microscopy. The evolution of microstructure for all studied blends was examined using Nikon polarizing microscope (Nikon Eclipse E600) equipped with hot-stage (Instec STC200). Small amount of polymer is placed between two microscopy glass slides as a sandwich and inserted to hot stage and melted at 200 [degree] C. After melting, thin film was obtained by applied small pressing on top glass slide (the thin film was approximately 0.05-0.1 mm in thickness). The blends samples were heated on the hot-stage from room temperature to 200 [degrees] C and then kept at 200 [degree] C for 3 min to erase their thermal history and finally cooled from 200 [degrees] C to a temperature where the growing of spherulites are started.


Wide Angle X-Ray Diffraction (WAXD). The crystalline phases were analyzed by wide-angle X-ray diffraction (WAXD) measured with Analytical PRO X'Pert-Holland, Cu-Ka radiations (A = 1.54178 A) in the range of 5-35 [degree] at 40 kV. The WAXD data for PHB/PLLA blends were obtained at room temperature (~25 [degree] C), with the scan rate of (2 [degree]) 2 [theta] mi [n.sup.-1] Film samples were cut into rectangular pieces (4 c [m.sup.2]) and mounted on the matrix before analysis.

FTIR Spectrometer. Infrared spectra were recorded with a Fourier Transform FTIR 6100 Jasco spectrometer in the wavenumber range 550-4000 c [m.sup.-1]. All spectra are recorded at room temperature. The films of the samples are cut into rectangular pieces (4 c [m.sup.2]).


Differential Scanning Calorimeter Analysis

DSC analyze used to identify the fundamental thermal reactions of blends. Figure 1 shows the relation between temperature and heat flow. One can seen the glass transition temperature (Tg) of pure PLLA appears at 70[degrees] C. In our previous work (1-3), we find that pure PHB has glass transition temperature of 5 [degrees] C. Increasing the weight percentage of PHB results in a gradual decrease of Tg, to 63 [degrees] C for B130 sample, 62 [degrees] C for BM0 sample and 61 [degree ] C for B310 sample. The second heating of all blends shows exothermic peaks related to the cold crystallization temperature ([]). The decrease of PLLA content in the blend provided an increase in []. According to the DSC results, the cold crystallization temperature ([T.sub.CC) of the samples B130 and B310 are 108 and 110 [degrees] C, respectively. In case of B110 there are two values for [] which are 108 and 121 [degrees] C The first peak is related to the PHB phase, whereas the second peak is to the PLLA phase. When the amount of PHB and PLLA are less than 25%, the blend is homogeneous and becomes immiscible at 50% PLLA. These results agree well with the previously reported results by Ozaki and coworkers (8) and Zhang et al. (27). It is interesting to note that both PHB/PLLA (25/75) and (75/25) samples exhibit two melting peaks (Tm) at 172, 180 and 174, 180CC, respectively. These peaks are attrib uted to recrystallizalion or two different lamella thickening. The melting peak ([T.sub.m]) appears brooding 180[degrees]C and shoulder at 172 [degrees] C in case of Bn0 due to the crystalliza tion process form the two types of lamella. These results are in agreement with the results of Wasantha et al. (28). Figure 2 shows the DSC results of the samples [B.sub.381], [B.sub.551], and [B.sub.831] with 9.1% of PVAc. The figure reveals that, the glass transition temperature appears at 60, 56, and 55 [degrees] C, cold crystallization ([]) at 108, 112, and 113 [degrees] C and melt ing point ([T.sub.m]) at 174, 175, and 175 [degrees] C. Also, the cold crystallization peak temperature ([]) moves to a higher temperature and becomes broader when PHB content is increased. The presence of one crystallization temperature suggests that PHB/PLLA blends significant single homogeneous phase throughout the heating process. By comparing the data of Figs. 1 and 2, it was noted that, the melting point becomes one peak and shifts to a lower temperature by addition of PVAc. This is due to the increase in the amorphous phase in both component.




Morphology of the Spherulites

The miscibility of blends was studied by POM. It is known that, large spherulitic material is more brittle than fine spherulite with the same percentage of crystallinity. Figure 3 shows the surface morphology of sample Bno. The microstructure was characterized by a Maltese cross-birefringent pattern spherulites. A sharp banded spherulite of PHB with the fibrils spherulite of PLLA was seen in the isothermally crystallized at 100 [degrees] C. It is clear from the image that, the PLLA spherulites are darker than the PHB spherulites, which suggested that PHB was crystallized faster than PLLA due to the higher crystallization rate of PHB. Two phase separations was found in the sample [B.sub.110] and this indicated that PLLA was not miscible with PHB. These results were discussed from DSC analysis in Refs. 29-33.

The Spherulitic morphology of blends, at various crystal tallization temperatures for the investigated samples [B.sub.381] (a) 120 [degrees] C, (a') 140 [degrees] C, sample [B.sub.551], (b) 120 [degrees] C, (b') 140 [degrees] C, sample [B.sub.831]l (c) 120 [degrees] C, and (c') 140 [degrees] C that formed as the nonbanded spherulite are shown in Fig. 4. By increasing the crystallization temperature, the number of spherulites was found to be reduces, whereas their size increases. The results also show that the blends were miscible after addition of 9.1% PVAc. Figure 5 shows spherulitic morphology of samples blends after annealed at 160 [degrees] C for 180 min and different crystallization temperatures, sample [B.sub.381] (a) 120 [degrees] C, (a') 130 [degrees] C, sample [B.sub.551] (b) 120 [degrees] C, (b') 130 [degrees] C, sample [B.sub.831] (c) !20 [degrees] C and (c') 130 [degrees] C. The shape of the spherulite is ring with twisting lamellae, like PE and PVDF. One can seen from Fig. 5c' that a sharp banded spherulite structure growing radially with a large radius from initiate (primary) nucleation site with closed circles. Figure 6 shows fibrils spherulite (nonbanded) of sample [B.sub.551] after melting and at different isothermal crystallization temperatures (a) 100 [degrees] C, (b) 110 [degrees] C, (c) 120 [degrees] C, (d) 130 [degrees] C with optical polarizer and (a') 100 [degrees] C (b') 110 [degrees] C, (c') 120 [degrees] C, (d') 130 [degrees] C without optical polarizer. POM without optical polarizer was used to illustrate the appearance of spherulite. In contrast, Fig. 7 shows POM graphs of sample [B.sub.551] with banded spherulites (ring). The sample of this blend was annealed at 160 [degrees] C for 180 min and isothermal crystallization temperature at 100 [degrees] C and 120 [degrees] C. The POM images (a) and (b) are measured with optical polarizer while the images (a') and (b') are measured without optical polarizer. The images without optical polarizer reveal ring spherulite. The morphology of sam ple [B.sub.551] prepared at isothermal crystallization temperature of 160 [degrees] C (600 min) and cooled to 120 [degrees] C was shown in Fig. 8. In the begin, the sample was melted and annealed at crystallization temperature of 160 [degree] C (600 min) until the fibrils spherulite is not completely grow and presence of space between spherulites (as in Fig. 8a and b). By reducing the temperature of crystallization to 120 [degrees] C and 110 [degrees] C, the banded (ring) spherulites are started to form. One can see the variation between fibrils spherulite and the ring (banded) spherulite. The POM image was measured with optical polarizer (a) while the image without optical polarizer (a'). This means that the two types of crystals depend on the crystallization process. The reason for this spiral is the tilting of the lamella by longer annealing time. Such twist on the sheaf leads to the formation of spiral, which can be observed in helicoidally twisted crystallites with a perfect spherulite around them. On the other hand, the banded or nonbanded spherulites morphology detected in samples [B.sub.381], [B.sub.551], and [B.sub.831] are strongly depending on the crystallization conditions. In general, there are several crystal polymorphs in the polymers. Some of these crystalline polymers take the form of various banded spherulites and nonbanded (fibrils spheru-lites) such as; isotactic polypropylene (PP) (34) and PVDF (35). Figure 9 shows other image of the morphology of B551 prepared at isothermal crystallization temperature of 160 [degrees] C (600 min) with different scale. From this image it can be observed that the lamella begin to form fibrils branches and splay apart from each other. As a result of continual splaying and branching of the lamellae, the initial lamella gradually developed into a lamella sheaf (Fig 5c'). L. J. Ping et al. (36) found two kinds of banded spherulites in PHB, which are formed at 100 and 115 [degrees] C. Many scientists also tried to interpret the crystal growth mechanisms of banded and fibril spherulites. So far, there are some models that have been accepted widely. One of these models proposed by Keller (37), Keith et al. (38), and Bassett et al. (39) that depends on the stress of twisting (rotation) lamellar crystal. Gan et al. (40) proposed two types of crystals with different structures formed in the banded spherulites. In addition, Owen et al (41) proposed a mechanism for twist banding, which could be due to the flexibility of bending and torsion twisted lamella as helix. These models could explain the mechanism of spiral twist and therefore, it should be suitable for many polymers especially for chirai polymers. Nevertheless, these models cannot explain all the phenomena that occur in the experiments generally, but only explain some special cases. It is known that spherulites of chirai polymers are banded polymers such as; polyepichlo-rhydrin (PECH) (42), PE [42J and PHB (3). In addition, there are chirai polyesters that it make helical conformations, i.e., the helices are left-handed like PHB and poly (3-hydroxybutyrate-co3-hydroxyvalerate) PHB-co-PHV.








FTIR Analysis

In our previous work, the vibration structure of the neat PHB were examined (1-3). In the present study, PLLA and PLLA with PHB blends were analyzed using FTIR spectroscopy (see Fig. 10). The neat PLLA and PHB were used for comparison (3, 7, 8). It is known that the C=0 stretching bands for PHB appeared at 1723 c [m.sup.-1] (3, 7, 8). Figure 10 shows that the C=0 stretching band occurs at 1752 c [m.sup.-1] for PLLA. Besides, the C=0 stretching band of samples [B.sub.130], [B.sub.110], and [B.sub.310] appears at 1750 c [m.sup.-1]1 with small change of wave number. On the other hand, the C=0 stretching band for samples [B.sub.130], [B.sub.110], and [B.sub.310] appears at 1744, 1726, and 1724 c [m.sup.-1]with a change of its position, respectively. Since the peaks at 1272 and 1226 c [m.sup.-1] are crystalline-sensitive bands for PHB and PLLA (7, 30), they are assigned to the C--O--C stretching bands of the crystalline parts and may be due to the helical structures. These peaks are appears as shoulder for PLLA as well as samples [B.sub.130], [B.sub.110] [B.sub.310], [B.sub.381], and [B.sub.551]. In contrast, the peak appears at 1272 c [m.sup.-1] in sample [B.sub.831] is a board peak similar to stretching band of PHB, since its peak intensity become stronger with the increase PHB content, i.e., the crystallnity increased with increasing PHB content. It has been reported (7, 30) that the bands at 1180 c [m.sup.-1] are assigned to the amorphous of C--O--C stretching bands for PHB, PLLA and their blends. Also, the C--O--C stretching band of PLLA and samples [B.sub.130], [B.sub.110], [B.sub.310], [B.sub.381] appears at 1083 c [m.sup.-1]. Besides, the C--O--C stretching band appears at 1097, 1093, and 1096 c [m.sup.-1] for PHB (3, 7, 8), B551 and B831, respectively. Additionally, the bands at 1048 c [m.sup.-1] are assigned to the C--CH3 stretching for PLLA, PHB and their blends (7, 30). What's more the peaks located at 1130 c [m.sup.-1] of PLLA, PHB and their blends were assigned to the stretching vibration of CH3 rocking (29). Figure 11 shows the FTIR spectra. It can be seen that the CH3 asymmetric deformation band at 1455 c [m.sup.-1] of PLLA, PHB (30), and their blends and [CH.sub.3] symmetric deformation band at 1366 for PLLA, and samples [B.sub.130], [B.sub.110], [B.sub.310]), and [B.sub.381]. ft also appears at 1376 c [m.sup.-1] for PHB (7, 30) and samples [B.sub.551] and [B.sub.831]. The peaks at 755 and 867 c [m.sup.-1] are distinguish between the crystalline and the amorphous phases of PLLA, and samples [B.sub.130], [B.sub.110], [B.sub.310], and [B.sub.381]. These peaks are shifted for samples [B.sub.551] and [B.sub.831] from 867 to 897 c [m.sup.-1]. It is also found that the intensity of both peaks is decreased. These results indicate that samples [B.sub.130], [B.sub.110], and [B.sub.310] are immiscible since no changes in the peaks positions of blends were observed. These means that there are no strong molecular interactions between PHB and PLLA were noted. It is interesting to note that the addition of PVAc to PLLA and PHB leads to shift the C=0 band and make dipoledipofe interactions between the C=0 group and the [CH.sub.3] group in PHB and PLLA. The spectra of samples [B.sub.551] and [B.sub.831]1 are similar to that of pure PHB [3]. All spectra of the samples [B.sub.130], [B.sub.110], [B.sub.310], and [B.sub.381] are very similar to the neat PLLA spectra.

Wide Angle X-Ray Diffraction Analysis

It is known that the crystalline structure of PHB is orthorhombic. The lattice parameters of PHB are: a = 0.572 nm and b = 1.312 nm with its chain conformation in the left-handed [2.sub.1] helix (1-3). PLLA can be crystallized from melting or solution as orthorhombic unit cell with a lattice parameters of a = 1.037 nm, b = 0.598 nm (43). It is acknowledged that ne PLLA was usually formed from the [alpha]-type [alpha] helix [10.sub.3]. PLLA can be form two-crystals clearly, depending on the crystallization conditions of [alpha] form with a [10.sub.3] helical shape (43-46) and [beta] form with a spiral shape [3.sub.1] (30, 45-47), In our previous studies (1-3), the WAXD of neat PHB has reflection peaks at 13.5 [degrees] and 16.7 [degrees] corresponding to (020) and (110) planes (1-3). Figures 11 and 12 show the WAXD analysis of all the samples. There are two sharp strong crystalline reflection peaks at 13.5 [degrees] and 16.7 [degrees] corresponded to the (020), and (110) planes and three other weakJy peaks at 19.1 [degrees] 22 [degrees], and 25.4 [degrees]. The two first peaks characteristics of typical [alpha]-form orthorhombic structure of PHB (1-3). The PLLA with only one broad diffraction peak (major peak) appeared at 2 [theta] of 16.7 [degrees] corresponding the (110/ 200) reflections (d = 0.536) and smaller peaks at 19.1 [degrees] and 32 [degrees] corresponding to (010) and (203) respectively. In Fig. 11, the maximum intensity of samples [B.sub.130], [B.sub.110], and [B.sub.310] ([alpha]-form crystal) occurs approximately at 2 [theta] = 13.5 [degrees], which corresponding to the basal spacing (d = 0.655, 0.655, 0.654 nm) of the (020) plane along with 2 [theta] = 16.6 [degrees], which corresponded to the basal spacing (d = 0.531, 0.532, 0.532 nm) of the (110) plane. Figure 12 also shows that the maximum intensity of samples [B.sub.381] [B.sub.551], and [B.sub.831] ([alpha]-form crystal) occurs at 2 [theta] = 13.5 [degrees], corresponds to the basal spacing (d = 0.660, 0.658, 0.657 nm) of the (020) plane and 2 [theta] = 16.6 [degrees], corresponds to basal spacing (d = 0.534, 0.533, 0.529 nm) of the (110) plane. Additionally, the maximum diffraction of the [B.sub.831] ([alpha]-form crystal) occurs at 2 [theta] = 13.5 [degrees]. In this case, the intensity was increased due to the increasing of crystallinity. Moreover, diffrac tion peak and 2 [theta] =16.6 [degrees] was shifted to higher angle of 16.8 [degrees] and its maximum intensity was increased, because the crystal structure was changed. Furthermore, the peak diffraction at 2 [theta] = 25.4 [degrees] and 22. 1 [degrees] increased in compari son to those of the samples [B.sub.381] and [B.sub.551]. The [beta]-form crystal was observed at 2 [theta] = 19.6 [degrees] for all samples, which corresponds to (110) plane and d = 0.465, 0.464, 0.464, 0.464, 0.469, and 0.448 nm (see Figs. 11 and 12). It can also be observed in Fig. 12 that the intensity of a-form diffraction at 2 [theta] = 13.6 [degrees] is increased, while the intensity of (020) diffraction of [beta]-form at 2 [theta] = 19.4 [degrees] remains unchanged. However, with increasing PHB content in blends, the intensities of large peak a-form at 2 [theta] = 13.5 [degrees] (020) and 2 [theta] = 16.7 [degrees] (110) are increased. This result means that some traces of [alpha]-form and [theta]-form crystalline structures of PHB and PLLA could be exist in blends. The lattice parameters are unchanged in samples [B.sub.130], [B.sub.110], and [B.sub.310]. This result suggests that each component of the blends forms its crystalline structure independently of the second component. In conclusion, the lattice parameters are changed in samples [B.sub.381], [B.sub.551], and [B.sub.831]. Furthermore, the WAXD results revealed that all (PHB/ PLLA) blends without PVAc are immiscible whereas, the (PHB/PLLA) blends with PVAc are miscible.




The effect of processing conditions on the development of morphological features of banded or nonbanded spherulites of PHB/PLLA blends (with and without PVAc addition) has been studied. The structure, morphology, crystallization, melting behavior and miscibility of PHB/PLLA blends have been investigated and analyzed using POM, DSC, WAXD and FTIR spectroscopy. The results show that, the blends with PVAc have two types of spherulites, produced at different crystallization temperatures. One of these spherulites is ring and occurs after annealing at high temperature (160 [degrees] C) and long annealing time (180 min), which results in tilting of the lamella consequence lamellar twisting. The second is fibrils, which is directly produced after melting and isothermal crystallization without annealing. This depends on the crystallization conditionsand thermal treatment. Further structural analyses revealed that no miscibility and phase separation were observed in the sample [B.sub.110].

DSC examination indicated that all blends are miscible, except the [B.sub.110], which is immiscible with having two cold crystallization temperatures.

FTIR analysis indicated that the PHB/PLLA blends without PVAc were immiscible, but the addition of PVAc to PLLA and PHB (in [B.sub.381] [B.sub.551] and [B.sub.831],) leads to shift the C=0 band and makes dipole-dipole interactions between the C=0 group and the [CH.sub.3] group in both of PHB and PLLA.

The diffraction analysis showed four a crystal diffraction peaks at {(020), (110), (121), and (040)} planes and one [beta] crystal diffraction peak at (021) plane. The lattice parameters are unchanged in samples [B.sub.130], [B.sub.110] and [B.sub.310] This result suggests immiscible blends, but the lattice parameters are changed in samples [B.sub.381], [B.sub.551], and [B.sub.831]. This result suggests miscible blends.


The author thanks SABIC company for petrochemicals (Research & Consulting Center) and Institute of Scientific Research for part supporting this Project.


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TABLE 1. The samples and composition of blends.

Sample code Composition (wt %)

PLLA       PLLA (100)
B130       PHB/PLLA/PVAc (25/75/0)
B110       PHB/PLLA/PVAc (50/50/0)
B310       PHB/PLLA/PVAc (75/25/0)
B381       PHB/PLLA/PVAc (22.7/68.1/9.1)
B551       PH/B/PLLA/PVAc (45.4/45.4/9.1)
B831       PHB/PLLA/PVAc (68.1/22.7/9.1)

Ahmed Mohamed El-Hadi Department of Physics, Faculty of Applied Science, Umm Al-Qura University, Saudi Arabia

Correspondence to: Ahmed Mohamed El-Hadi; e-mail: Bioplastics.

Ahmed Mohamed El-Hadi is permanently at Department of Basic Science, Higher Institute for Engineering and Technology, El Arish, North Sinai, Egypt. DOI I0.1002/pen.21991

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Author:El-Hadi, Ahmed Mohamed
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Date:Nov 1, 2011
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